Adding Stickler CI config

[stickler-ci]

Your stickler.yml configuration file could not be parsed. We got the following error:

while parsing a block mapping
  in "<string>", line 1, column 1:
    linters:
    ^
expected <block end>, but found '<block mapping start>'
  in "<string>", line 4, column 3:
      csslint: {  }
      ^